The present invention relates to the reduction of the moisture content of coal and, more particularly, to a composition and a method of treating coal with the composition to reduce the moisture content of the coal.
Most electric utilities east of the Mississippi River have boilers designed for burning coal having a lower moisture content than is generally found in coal from the western United States. For these utilities, or other users of coal having boilers designed for low-moisture coal, to use western coal without derating the boilers, a portion of the inherent moisture of the coal must be removed. The benefits of drying high-moisture, low-sulfur western coal are:
(1) lower transportation costs,
(2) improved burning qualities of the coal,
(3) lower boiler operating and maintenance costs, and
(4) increased boiler capacity.
The known methods for drying coal are both thermal methods. One such thermal drying process uses a roto-louvre dryer to dry 3/4 inch coal to a moisture content of 10 to 15 percent. The coal is subjected to a temperature of 400.degree. C. to achieve drying, cooled using ambient temperature air, and then coated with oil or another sealant to prevent the reabsorption of water. A second method is similar to the first except that the coal is subjected to gas heated to about 260.degree. C. to achieve drying. Coating of the coal after drying is also necessary in the second method. These methods have significant problems. First, dust control during drying and before sealing is a significant problem. Second, these severe drying methods can result in the loss of low boiling volatile hydrocarbons, nitrogen, carbon monoxide, and carbon dioxide from the coal. Neither the dust nor the low boiling hydrocarbons can be vented to the atmosphere without causing serious environmental problems. Normally, they are controlled using expensive environmental equipment.
The present invention provides a composition and a method for reducing the moisture content of coal which achieves the desired advantages without the aforementioned disadvantages. The moisture content of coal can be reduced by 50 percent or more with the method of this invention. Surprisingly, the moisture reduction is accomplished by adding to the coal an aqueous solution which is then evaporated, leaving a residue of polyethylene oxide. Another advantage of using polyethylene oxide solutions in the present method is that it avoids the tendency of high moisture low-rank coal to slack or degrade in size when it is being dried.
Bureau of Mines Report of Investigations No. 8349 entitled "Flocculation Dewatering of Florida Phosphatic Clay Wastes" by Annie G. Smelley and I. L. Feld, published in 1979 by the United States Department of the Interior, discloses the use of polyethylene oxide as an organic flocculant to assist in the disposal of phosphatic clay wastes and reclaiming mined land. Such clay wastes are difficult to remove from water because of their colloidal properties. When polyethylene oxide is added to such a colloidal suspension, it causes the clay wastes to agglomerate into a coherent plastic mass and up to 94 percent of the water can be removed in the form of a clear liquid. High molecular weight polyethylene oxide has also been used as a flocculant for coal flotation tailings (Chemical Abstracts, Vol. 82, p. 142463, abstract 142458X). The above uses of polyethylene oxide are clearly distinguishable from the present invention since solids are agglomerated and removed from primarily liquid systems whereas in the present invention, moisture is removed from a primarily solid system.